EP 1 229 985 B1 discloses a fluid filter having a housing in which there is a receiving space for receiving a ring filter element, said space being closable by a cover. Furthermore, an inlet for crude fluid, an outlet for cleaned fluid and an outlet through which the receiving space can be emptied on removal of the cover are also provided. This outlet is at the bottom of the receiving space in the installed state of the fluid filter. In addition, a closure is provided on the ring filter element for closing the outlet when the ring filter element is inserted into the receiving space and the receiving space is closed by the cover. With the known fluid filter, said closure is formed by a journal arranged eccentrically to protrude axially away from the ring filter element. With the known fluid filter, the receiving space is closed by the cover from above, and the outlet is provided at the bottom of the receiving space in the housing. With the known fluid filter, to simplify locating and inserting the journal into the outlet, a concentrically arranged and helically ascending ramp is provided on the housing, such that the outlet is arranged between a lower end of the ramp and an upper end of the ramp. When the cover is screwed in place, the journal locates the outlet automatically and can penetrate into it and close it due to the rotational movement of the ring filter element and due to the journal sliding along the ramp. In an especially advantageous embodiment of the known fluid filter, the ramp and the journal can work together according to the lock-and-key principle in such a way that only a ring filter element provided with a journal adapted to the ramp can be used with the known fluid filter, such that the closure locates the outlet automatically and closes it when the cover is screwed into place.
DE 200 06 972 U1, DE 200 08 112 U1 and WO 00/62893 A1 disclose other fluid filters with which the cover closes the receiving space from underneath in the installed state such that the cover has the outlet arranged concentrically with the longitudinal central axis of the ring filter element and is closed from the outside by a closure in the form of a screw designed as a separate component. Before removing the cover, the receiving space can thus be emptied by removing the closure.